Production of fuel oils



United States Patent 3,303,128 PRODUCTION OF FUEL OILS David Hallam Peel and James ODonnell, Sunbury-on- Thames, England, assignors to The British Petroleum Company Limited, London, England, a corporation of England No Drawing. Filed June 18, 1964, Ser. No. 376,221 Claims priority, application Great Britain, July 16, 1963, 28,104/ 63 2 Claims. (Cl. 208366) This invention relates to the production of fuel oils from residues obtained by the vacuum distillation of waxy crude oils. In particular it rel-ates to the production of fuel oils having a viscosity in the range 40 to 90 cs. at 75 C. and a maximum pour point of 70 F.

In Great Britain, customer specifications for fuel oil viscosities are usually expressed in terms of Redwood 1 seconds at 100 F. However, where at 100 F. solid material such as wax is present suspended in the oil it is not possible to determine the true viscosity experimentally at 100 F. -It is necessary in such a case to carry out viscosity determinations at temperatures at which all normally solid materials are dissolved in the oil and to extrapolate back to give a figure for the true viscosity at 100 F. The above fuel oil viscosity specification of 40 to 90 cs. at 75 C. with which we are concerned in the present application is, in fact, the same as a specification of 1000 to 3500 Redwood 1 seconds at 100 F.

Fuel oils may be prepared from high viscosity vacuum residues by blending the residue with a low viscosity diluent, or cutter .stock, such as gas-oil, the proportion of diluent depending upon the duel oil viscosity required. Vacuum residues from a large variety of crudes which do not contain excessive quantities of wax when prepared by normal refinery practice have an equivalent cut point of less than 550 C. corrected to 760 mm. Hg. Generally these residues when blended with the necessary amount of gas-oil to give the required viscosity, yield a fuel oil having a pour point below the specified maximum of 70 F. Vacuum residues obtained by distilling very waxy crudes to a cut point of less than 550 C., however, for example some Libyan and Nigerian crudes, will not blend with gas-oil to give both the required viscosity and a pour point below 70 F. In order to obtain the required pour point these residues have to be blended with so much gasoil that the viscosity of the resulting blend is less than the specified 40 cs. (1000 Redwood 1 seconds).

In this specification Waxy crude means a crude oil which contains wax in an amount such that, when conventionally distilled in refinery distillation units to an equivalent cut-point of less than 550 C. corrected to 760 mm. Hg, it gives a vacuum residue having so high a wax content that it cannot be blended with gas oil to give a blend having a viscosity above 40 cs. at 75 C. (1000 Redwood 1 seconds at 100 F.) as well as a pour point below 70 F.

According to the present invention a process for the 3,303,128 Patented Feb. 7, 1967 production of a fuel oil having a viscosity within the range 40 to 90 cs. at C. and a maximum pour point of 70 F. from a Waxy crude comprises vacuum distilling the waxy crude to obtain a final vacuum residue boiling above 550 C. at a pressure corrected to 760 mm. Hg and blending this heavy residue with gas-oil to give both the required viscosity within the range 40 to cs. at 75 C. and a pour point below 70 F. The cut-point of the residue is preferably as close to 550 C. as is possible consistent with giving a residue which can be blended to give fuel oils of the required specification. The maximum cutpoint temperature is below that at which cracking of the feedstock commences. This point will vary from crude to crude but is readily determinable by experiment, for example, for a Nigerian crude the maximum cut-point obtainable without cracking is 595 C. and with a Libyan crude the maximum cut-point is 620 C.

Surprisingly, it has been found that the blending of these heavy, viscous residues with sufiicient gas-oil to give fuel oils having viscosities within the specified range also gives pour points below 70 F. The presence of paraffin wax is a contributory factor toward high pour points. Although the wax content of residues expectedly decreases with increasing cut-point, the heavy residues still contain large amounts of wax. Surprisingly, however, it has been found that the deleterious effect of the wax on the pour point of fuel oils blended from heavy residues having cut-points greater than 550 C. is not as severe as would be expected from the actual wax content. It is believed that the hydrocarbon type of the waxy components in distillates derived \from waxy crudes changes from predominantly straight-chain to branchedchain hydrocarbons, which may also contain ring structures, as the boiling points of the distillates approach 550 C. It is thought that the decrease in concentration of straight-chain hydrocarbons remaining in the residue is responsible for improved pour points of fuel oils obtained therefrom.

The invention is illustrated with reference to the following example.

ICC

Example Vacuum residues were obtained with cut-points in the range equivalent to 550 to 595 C. at atmospheric pressure by redistilling, at 0.2 mm. Hg pressure, a longer residue obtained from Nigerian crude oil. Vacuum residues were also obtained with cut-points in the range 550 to 620 C. by distilling, at 0.2 mm. Hg, a residue prepared by laboratory batch distillation of a Libyan crude oil. Inspection data on these residues and on a typical catalytically cracked gas-oil cutter stock are given in the following Table 1. Inspection data on blends of these residues with various proportions of this gas-oil cutter stock are given in the following Table 2.

It is seen from Table 2 that fuel oil blends having both the required viscosity and low pour point are readily obta-inable by blending a heavy residue of sufliciently high cut-point with gas-oil.

TABLE 1 Kinematic Viscosity cs. at- Wax Content TBP PPouir Com onent Out oin p point, Percent Melting F.

0. F. 210 F. 300 F. Wt. lloint,

Li ht Cat. Cracked Gas O 3.0 Ni gerian Residue 550 5,890 978 76.9 13. 5 D 575 16, 630 2, 229 127. 2 12. 5 162.9 10. 9 3 94. 7 24. 8 172. 6 22. 4 649 22. 1 1, 343 18.8

TABLE 2 Kinematic Viscosity cs. at Viscosity Red- 'IBP Proportion of wood 1 Cut residue in seconds at Pour Residue point, blend with 100 F. Point,

C. cutter stock, 100 F. (Calculated F percent wt. 170 F 210 F. (Extrapolated) from kinematic viscosities) Nigerian 550 67 62. 26. 7 560 2, 300 75 61 37. 8 17. 8 280 1, 140 55 Libyan 550 71 101. 4 44. 2 820 3, 300 90 66 63. 7 31. 8 360 1, 470 70 62 47. 0 23. 9 260 1, 060 65 Do ca. 620 61 91. 2 41.8 0 650 50 51 44. 7 23. 4 22 900 45 We claim: 25 quired viscosity Within the range 40 to 90 cs. at 75 C.

1. A process for the production of a fuel oil having a viscosity within the range 40 to 90 cs. at 75 C. and a pour point below F; from a waxy crude, such crude containing wax in an amount that, when conventionally distilled in refinery distillation units to an equivalent cut point of less than 550 C. corrected to 760 mm. Hg, it

gives a vacuum residue having so high a wax content that it cannot be blended with gas-oil to give a blend having a viscosity above 40 cs. at C., 1000 Redwood 1 seconds at 100 F., as well as a pour point below 70 F., comprising vacuum distilling the waxy crude to obtain a final vacuum residue boiling above 550 C. at a pressure corrected to 760 mm. Hg, and blending this heavy residue with gas-oil in an amount sufficient to give both the reand a pour point below 70 F.

2. A process as claimed in claim 1 wherein the vacuum distillation is conducted to give a residue having a cutpoint as close to 550 C. as is possible consistent with giving a residue which can be blended to give fuel oils of both the required viscosity within the range 40 to cs. at 75 C. and a pour point below 70 F.

References Cited by the Examiner UNITED STATES PATENTS 2,663,675 12/1953 Ewell t 208-l5 3,234,118 2/1966 Chen 20815 P. E. KONOPKA, Assistant Examiner.

DANIEL E. WYMAN, Primary Examiner. 

1. A PROCESS FOR THE PRODUCTION OF A FUEL OIL HAVING A VISCOSITY WITHIN THE RANGE 40 TO 90 CS. AT 75*C. AND A POUR POINT BELOW 70*F. FROM A WAXY CRUDE, SUCH CRUDE CONTAINING WAX IN AN AMOUNT THAT, WHEN CONVENTIONALLY DISTILLED IN REFINERY DISTILLATION UNITS TO AN EQUIVALENT CUT POINT OF LESS THAN 550*C. CORRECTED TO 760 MM. HG, IT GIVES A VACUUM RESIDUE HAVING SO HIGH A WAX CONTENT THAT IT CANNOT BE BLENDED WITH GAS-OIL TO GIVE A BLEND HAVING A VISCOSITY ABOVE 40 CS. AT 75*C., 1000 REDWOOD 1 SECONDS AT 100*F., AS WELL AS A POUR POINT BELOW 70*F., COMPRISING VACUUM DISTILLING THE WAXY CRUDE TO OBTAIN A FINAL VACUUM RESIDUE BOILING ABOVE 550*C. AT A PRESSURE CORRECTED TO 760 MM. HG, AND BLENDING THIS HEAVY RESIDUE WITH GAS-OIL IN AN AMOUNT SUFFICIENT TO GIVE BOTH THE REQUIRED VISCOSITY WITHIN THE RANGE 40 TO 90 CS. AT 75*C. AND A POUR POINT BELOW 70*F. 